1. Field of the Invention
The present invention relates to a fuel cell stack that generates electricity by an electrochemical reaction, and more particularly, it relates to a planar fuel cell stack having generators arranged in a plane surface.
2. Description of the Related Art
A fuel cell is a generator that generates electrical energy by an oxidation reaction of a fuel and a reduction reaction of an oxidizing agent. Fuel cell can be classified as a polymer electrolyte membrane fuel cell or a direct oxidation fuel cell according to the type of fuel used.
The polymer electrolyte membrane fuel cell is supplied with a reformed gas that is reformed from a liquid fuel or a gas fuel, and an oxidant gas such as air. In addition, the polymer electrolyte membrane fuel cell generates electrical energy by an oxidation reaction of the reformed gas and a reduction reaction of the oxidant gas. Such a polymer electrolyte membrane fuel cell has superior output characteristics, and can operate at a relatively low temperature. In addition, the polymer electrolyte membrane fuel cell has fast starting and response characteristics. Therefore, the polymer electrolyte membrane fuel cell is widely used as a power source for vehicles, a distributable power source for buildings, and a compact power source for electronic devices.
The direct oxidation fuel cell receives a liquid fuel and an oxidant gas (e.g., air), and generates electrical energy by an oxidation reaction of the fuel and a reduction reaction of the oxidant gas.
A typical fuel cell includes a generator which is a primary unit that generates electrical energy. The generator includes a membrane-electrode assembly (MEA) and separators disposed at opposite sides of the MEA. In addition, a plurality of the generators can be consecutively arranged, forming one stack.
A conventional fuel cell stack has a plurality of generators cascaded in series. This type of fuel cell stack requires multiple generators for a high output fuel cell stack, and accordingly, the stack becomes thicker.
A planar fuel cell stack having generators arranged on a plane surface has been suggested. However, the planar fuel cell stack has a relatively large planar area to thickness ratio so that it is difficult to fasten the generators and fastening plates that protect the generators with substantially uniform conjoining pressure. Furthermore, the planar fuel cell stack generators, the fastening plates and the separators are often made thinner to reduce overall weight of the stack. Then, conjoining pressure at locations removed from fastening points becomes relatively weaker than conjoining pressure at locations closer to the fastening points, causing gaps to be formed between the MEAs and the separators. Moreover, since oxidant holes are made on the fastening plate to allow external air to reach a cathode electrode of the MEA, the fastening plate becomes even harder to be fastened to the separators with uniform pressure.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.